Method for verifying dynamically a multiple beam antenna placed on a vehicle

ABSTRACT

A method for dynamically verifying a multiple beam antenna placed on a craft including a device for determining the position and course of the craft and a transmitter that via the antenna can emit pulsed signals. At least two transponders are placed in different directions round a measuring area with each transponder receiving a pulsed signal of at least one frequency, different for the different transponders, from the antenna. The transponders are adapted to send, after receiving the pulsed signal, a corresponding pulsed signal to the measuring station in such a manner that the transponder sending the signal can be determined at the measuring station which evaluates how well the antenna has managed to direct the radiated energy in the desired directions.

This is a nationalization of PCT/SE03/00591 filed Apr. 11, 2003 andpublished in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for dynamically verifying amultiple beam antenna placed on a craft. The method has been developedbased on problems in building a military jamming system, but may ofcourse be used in any other case where it is desirable to verify theproperties of a multiple beam antenna.

2. Description of the Related Art

A military jamming system must be able to direct much radiated energy inprecise directions round the transmitting antenna. The directions mustbe able to shift quickly. When such a system is built up or provided, itmust, like in other cases, be possible to verify the properties of thecomponents included by testing. Such a system comprises on the one handa multiple beam antenna and, on the other hand, equipment forcalculating and generating pulses in predetermined directions.

In a multiple beam antenna system, the emitted energy can be controlledby selecting one of a large number of transmitting beams. In order todirect the beam in the correct direction, information about position andheading of the antenna must be available. If the antenna is placed on acraft, instantaneous information is required.

Testing of a multiple beam antenna may take place in steps. A first testcan be performed in a laboratory environment. After mounting in a craft,however, the antenna must finally be be tested under dynamic conditions,i.e. while the craft is moving.

SUMMARY OF THE INVENTION

The present invention relates to a method of verifying a multiple beamantenna placed on a craft, such as a ship. In such tests, the functionof the antenna is verified under various sea conditions. A stabilisingsystem, if any, will then also be fully tested.

A special problem arises when it is desirable to verify data of amultiple beam antenna when the equipment for calculating and generatingpulses is not available. In this case, some kind of provisional solutionmust be prepared, allowing the function of the multiple beam antennaitself to be verified. The object of the present invention is to solvethis problem.

Accordingly, the present invention is directed to a method fordynamically verifying a multiple beam antenna which is placed on a craftincluding a device for determining the position and course of the craftand a transmitter device which, via the antenna, can emit pulsedsignals. Multiple transponders are placed in different directions rounda measuring area within which the craft is intended to move, with eachtransponder being adapted to receive a pulsed signal of at least onefrequency, different for the different transponders, via a receivingantenna which is capable of receiving incoming signals from the entiremeasuring area. A common measuring station is placed in connection withthe measuring area, with the transponders being adapted to send, afterreceiving the pulsed signal, a corresponding pulsed signal to themeasuring station in such a manner that it can be determined at themeasuring station from which transponder each received signal comes. Thecraft is made to move within the measuring area, with the position andcourse of the craft being determined before a measuring sequence, with ameasuring sequence being emitted from the craft via the antenna that isto be verified. The measuring sequence includes a reference signal fromthe craft to the measuring station, a first pulsed signal to the firsttransponder, a second pulsed signal to the second transponder etc., withthe measuring station detecting the reference signal and the subsequentpulsed signals from the transponders. The measuring procedure isrepeated while the craft is moving within the measuring area, and themeasuring station calculates to what degree the antenna manages todirect signals in different directions round the craft for differentfrequencies.

Also according to the present invention, the different transponders canemit signals to the measuring station within different, mutuallyneighbouring, narrowband frequency ranges.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toaccompanying drawing, in which

FIG. 1 shows a preferred embodiment of a ship's unit that is used in theinvention,

FIG. 2 shows a preferred embodiment of a transponder that is used in theinvention.

FIG. 3 shows a preferred embodiment of a measuring station that is usedin the invention.

FIG. 4 shows a conceivable appearance of what is shown by a spectrumanalyser (to the left) and an oscilloscope (to the right) whilemeasuring according to the invention, and

FIG. 5 shows what the geometry may look like round a ship whilemeasuring according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

The invention is used to verify a multiple beam antenna that is placedon a craft. The craft has a device for determining its position andcourse and a transmitter that is able to emit pulsed signals via theantenna. The craft is intended to move within a predetermined measuringarea. More than one transponder, in an example that will be describedhere four transponders, are placed in different directions round themeasuring area. Each transponder is adapted to receive a pulsed signalof at least one frequency which differs between the differenttransponders. The transponders are provided with a receiving antennathat is capable of receiving incoming signals from the entire measuringarea. Furthermore, a common measuring station is placed in connectionwith the measuring area.

The transponders are adapted to send, after receiving said pulsedsignal, a corresponding pulsed signal to the measuring station. The timesequence of the signals may be used to distinguish the different signalsat the measuring station. In a particularly suitable embodiment of theinvention, the transponders emit signals to the measuring station withindifferent, mutually neighbouring, narrow-band frequency ranges. In thisway, the signals from different transponders will meet essentially thesame wave propagation conditions on their paths to the measuring stationAt the same time the different frequencies of the signals giveadditional security when the signals are to be distinguished. In thiscase, a spectrum analyser may be used at the measuring station foranalysing the signals. In the following examples, it is assumed thatthis technique involving different frequencies is used.

The craft is made to move within the measuring area, and the positionand course of the craft are determined before a measuring sequence. Ameasuring sequence comprising a reference signal from the craft to themeasuring station, a first pulsed signal to the first transponder, asecond pulsed signal to the second transponder etc. are emitted from thecraft via the antenna that is to be verified. The reference signal andthe subsequent pulsed signals from the transponders are detected at themeasuring station. While the craft is moving in the measuring area, anumber of measuring sequences are emitted. Finally, measuring andcalculating equipment at the measuring station calculates to what degreethe antenna manages to direct signals in different directions round thecraft for different frequencies.

The ship's unit is the unit controlling the entire testing process. Theheart of the unit is a computer. FIG. 1 shows a preferred embodiment ofthe ship's unit where the computer 1 receives position data 2 in theform of GPS data and course of the ship continuously (for instance at arate of 100 Hz). For each set of transponder positions, which may be thesame for a long period of measuring, the GPS coordinates of thetransponders are manually input in the computer as target data 3, i.e.positions to which the emitted energy is to be sent.

The computer 1 controls a frequency synthesizer 4 and a pulse generator5 via a data bus, for instance a GPIB interface. The pulse generatorcontrols a microwave switch 6 which generates microwave pulses of apredetermined length. A pulse sequence in which the different pulseshave different frequencies is output from the microwave switch. Thecomputer gives a control command (directional information) 7 to themultiple beam antenna 8 for each output pulse, based on the position andcourse of the ship and the position of the different transponder units.The system provides for a predetermined frequency to be sent to aselected transponder unit. Owing to the fact that both side bands can beutilised in the transponder units, two frequencies can be sent to eachtransponder unit.

To be able to observe received signals at the measuring station, theemitted pulse repetition frequency PRF must be adapted to the currentgeometry of the test. The difference in path of propagation between thedifferent signal paths is dimensioning or the highest possible PRF thatcan be used.

FIG. 2 shows a transponder. The transponders consist of an omniantenna9, a frequency stable oscillator 10, for instance a DRO (DielectricResonance Oscillator), for frequency conversion via a mixer 11, aband-pass filter 12, a power amplifier 13 and a directional antenna 14.The transponder has a unique frequency at which it operates and which isdetermined by the frequency of the oscillator. All transponders convertthe input frequency to a frequency close to 12 GHz (separated about 10MHz) which is linked on to the measuring station.

The receiving antenna 9 should have a beam that covers the currentgeometry of the ship movements provided by the target path. A simpleamniantenna is a suitable alternative since the antenna gain shouldnormally not constitute a problem. The transmitting antenna 14 suitablyconsists of an antenna horn with a narrow beam. This is feasible whenonly a fixed connection between two points is involved.

The received signal is mixed down or up to about 12 GHz which is sent onto the centrally arranged measuring station.

By selecting suitable frequencies, the multiple beam antenna can betested over the entire frequency range and at optional angles. The tablebelow indicates the frequency f_(DRO) of the transponders, the testedfrequency of the multiple beam antenna and the frequency for thetransmission between transponder and measuring station.

Multiple beam Multiple beam antenna Transmitted antenna Transmittedf_(DRO) frequency frequency frequency frequency [GHz] [GHz] [GHz] [GHz][GHz] 5.02 17 11.98 7 12.02 4.04 16 11.96 8 12.04 3.06 15 11.94 9 12.062.08 14 11.92 10 12.08

The reference signal of the craft to the measuring station can be sentat, for instance, 12.4 GHz. The different frequencies make it possibleto distinguish in the measuring unit the reference signal, which isthere used as a trigger signal, and the different transponder signals.When the frequency sequence is known, the composition of receivedsignals will allow identification of which transponder has possibly notemitted the correct signal.

In measuring, the reference signal may be used to start a counter thatcontinuously counts the number of received pulses per reference pulse.This results in statistical data indicating the average of number oferrors in the directioning of the multiple beam antenna.

FIG. 3 shows an embodiment of the measuring station. The measuringstation consists of an omniantenna 15, a preamplifier 16, a directionalcoupler 17, a spectrum analyser 18, a frequency stable oscillator 20 forfrequency conversion by means of a mixer 19, a power divider 21, aband-pass filter 22, a detector 23, an oscilloscope 24, a band-passfitter 25 and an amplifier 26 of the type Detector Loop Video Amplifier(DLVA). The reason why there is a conversion step in the measuring unitis the much greater selectivity that can be obtained since it is easierto separate reference signal and measuring signals by using steepfilters.

The receiving unit converts the signal down to base band (in this caseabout 1 GHz). It is then possible to see in an oscilloscope whichposition does not function every time. By letting the spectrum analyserbe set for integration of a number of sweeps, the level of eachfrequency component may represent how many of the outputs go wrong. Thisimplies that the transponder units are adjusted in amplitude, so thatthe answers will be equal in terms of amplitude.

FIG. 4 shows a conceivable appearance of what is shown by the spectrumanalyser (to the left) and the oscilloscope (to the right).

FIG. 5 shows what the geometry may look like round a ship whose multiplebeam antenna is to be verified. The ship is designated F, thetransponders A, B, C, D and the measuring station M. When testing, thetransmission between transponder and measuring station must takemultipath propagation into consideration so that fade-out does not takeplace at the frequency used. The height of the antenna adjacent to thetransponder must be adjusted (small differences in height in a decimetrerange are involved). This can be carried out in advance.

The system operates in a sequence that repeats itself continuously. Theinput values are the coordinates of the transponder units and theirfrequency channels, see Table 2.

Coordinate Frequency 1 [GHz] Frequency 2 [GHz] Reference unit X_(R),Y_(R) 12.4 — Transponder A X_(A), Y_(A) 17 7 Transponder B X_(B), Y_(B)16 8 Transponder C X_(C), Y_(C) 15 9 Transponder D X_(D), Y_(D) 14 10

The testing sequence is as follows:

-   -   1. For each measuring sequence a set of navigation data is used,        consisting of the current GPS position of the ship, as well as        its course. Navigation data is used to calculate output        directions towards each transponder unit and the reference unit.    -   2. The frequency synthesizer is directed to the reference        frequency, and the pulse generator (which is set for generation        of bursts of pulses) is triggered. The interval between the        pulses in the burst is adjusted to the current geometry so that        the received pulses at the measuring stations do not overlap.    -   3. The reference signal is sent from the multiple beam antenna        to the measuring unit. There the signal is detected in the        special channel that has a fairly narrow band-pass filter for,        in this example, 12.4 GHz. The detected pulse gives a trigger        pulse that is input in the oscilloscope and other recording        equipment.    -   4. The frequency synthesizer is quickly shifted to the first        frequency (17 GHz) which is sent to the transponder A.    -   5. The pulse is received by an omnidirectional antenna 9 in the        transponder A and is converted to essentially 12 GHz (11.98        GHz). The pulse is amplified and sent via a arrow beam x-band        horn antenna 13 that is directed to the measuring station M.    -   6. The measuring station receives the 12 GHz signal from the        transponder A, which is detected in a DLVA (Detector Loop Video        Amplifier). The video signal from the DLVA is sent on to the        oscilloscope and other recording equipment.    -   7. The frequency synthesizer is quickly shifted to the second        frequency (16 GHz) which is sent to the transponder B.    -   8. The pulse is received by an omnidirectional antenna 9 in the        transponder B and is converted to essentially 12 GHz (11.96        GHz). The pulse is amplified and sent via a narrow beam x-band        horn antenna 13 that is directed to the measuring station M.    -   9. The measuring station receives the 12 GHz signal from the        transponder B, which is detected in a DLVA. The video signal        from the DLVA is sent on to the oscilloscope and other recording        equipment.    -   10. The same procedure for transponders C and D. Subsequently        transmission at the lower frequencies to transponders A to D        begins.    -   11. The measuring station M has received a total of 9 pulses and        presented these on the oscilloscope and recorded them in, for        instance, a measuring computer with data collecting equipment.    -   12. After a certain time, the procedure starts once more after        new navigation data for the ship has been input.

The invention may also advantageously be used when testing airbornejamming transmitters with electrically controlled antennas. Thedifference is that this is a more complicated scenario. For calculation,also the height coordinates must be used. When testing for flyingtargets, the number of targets should be limited to one, or possiblytwo. The targets that are to be illuminated with jamming energy mayconsist of, for instance, helicopters provided with transponders.

The difference in connection with flying targets is that the link to themeasuring unit must have an omnidirectional antenna. Moreover, thecurrent position of the target must be linked to the jamming aircraft ata communication frequency.

The invention being thus described, it will be apparent that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be recognized by one skilled in the art areintended to be included within the scope of the following claims.

1. A method for dynamically verifying a multiple beam antenna which isplaced on a craft comprising a device for determining the position andcourse of the craft, a transmitter device which via the antenna can emitpulsed signals, and a plurality of transponders placed in differentdirections round a measuring area within which the craft is intended tomove, each transponder being adapted to receive a pulsed signal of atleast one frequency, different for the different transponders, via areceiving antenna which is capable of receiving incoming signals fromthe entire measuring area, a common measuring station being placed inconnection with the measuring area with the transponders being adaptedto send, after receiving said pulsed signal, a corresponding pulsedsignal to the measuring station in such a manner that it can bedetermined at the measuring station from which transponder each receivedsignal comes, the craft moving within the measuring area with theposition and course of the craft being determined before a measuringsequence, said measuring sequence being emitted from the craft via theantenna that is to be verified, said measuring sequence including areference signal from the craft to the measuring station, a first pulsedsignal to the first transponder, and a second pulsed signal to thesecond transponder with the measuring station detecting the referencesignal and the subsequent pulsed signals from the transponders, saidmeasuring procedure being repeated while the craft is moving within themeasuring area, and said measuring station calculating to what degreethe antenna directs signals in different directions round the craft fordifferent frequencies.
 2. The method as claimed in claim 1, wherein thedifferent transponders emit signals to the measuring station withindifferent, mutually neighbouring, narrow-band frequency ranges.